This invention relates generally to a reset circuit for use with a microprocessor or other integrated circuit device. More specifically, this invention relates to a reset circuit for generating a signal which resets elements in the device after a power supply is powered-up to a voltage sufficient for proper operation.
Microprocessors are powered by an external power supply which provides a range of voltages. When the power supply is initially turned on, the logic states of the electrical elements in the microprocessor must be initialized. After the states have been initialized and the chip is operating, the power may for some reason dip, causing the electrical components to change state or otherwise operate improperly. It is then necessary to reset the states of the circuitry when the power reaches a voltage sufficient to permit proper microprocessor operation.
In the past, off-chip reset circuits have been employed to initiate the resetting of the circuitry when the power supply reaches a sufficient voltage to permit proper operation. However, these off-chip circuits are undesirably large and utilize valuable circuit board space. With the advance of technology, microprocessor reset circuits have been developed which are implemented as part of the device chip, thereby obviating the use of an external pin for reset circuitry. However, electromagnetic interference has been found to sometimes undesirably affect operation of existing such resets circuits and cause the microprocessor to initially be in unknown states.
It is therefore a general object of the invention to provide a novel microprocessor reset circuit which will obviate or minimize difficulties of the type previously described.
It is a specific object of the invention to provide a microprocessor reset circuit which will reliably generate a reset signal when the power supply is "powered-up".
It is another object of the invention to provide a microprocessor reset circuit which may be implemented on a microprocessor chip.